International patent application No. WO 2005/061445 (Langstrom et al.) (1) and references cited therein are describing carbonylation via isocyanate using azides and carbon monoxide. This reaction is promoted by a transition metal complex (e.g rhodium, palladium) and is performed in a high pressure reaction chamber. The main features of Langstrom's and similar methods are as follows: Introduction of carbon monoxide into the reaction chamber via the gas inlet and introduction at high pressure an azide solution mixed with a transition metal complex and a liquid reagent (solvent) into the reaction chamber via the liquid inlet. Since Langstrom method is dealing with carbon-isotope monoxide, additional technical measures have to be undertaken for trapping the carbon-isotope dioxide and converting it to carbon-isotope monoxide.
Obviously, these reactions require very special equipment, alkyl azide solution, expensive transition metal complex and hazardous highly toxic gas—carbon monoxide.
In contrast to this kind of procedure, the present method utilizes an alkyl azide solution, inexpensive compound of trivalent phosphorous (e.g. triphenylphosphine) and trialkylammonium hydrogen carbonate buffer. This buffer is prepared by simple bubbling of harmless carbon dioxide in a mixture of trialkylamine and water until pH about 7-8 is reached. The carbamoylation reaction itself is then performed in a tightly closed vessel, like, e.g, a bottle with a screw cap.
It is noteworthy that the present procedure is extremely simple. It does not require any special equipment (unlike Langstrom's (1) or similar procedures), any expensive transition metal complexes or, more importantly, a hazardous highly toxic gas—carbon monoxide. In other words, the present procedure may be carried out in any chemical laboratory.